Some of image reading apparatuses for reading an image of a source document have a function to automatically clip out only a source document image, from the image that has been read (automatic cropping). Generally, the automatic cropping function is configured to detect an inclination of the source document image when performing the cropping, when the source document placed on a document table is tilted, correct the inclination of the source document image clipped out, and display or store the corrected image. Patent Literature (PTL) 1 discloses a method of clipping out a source document image from an image read by an image reading apparatus, detecting an inclination of the source document image, and correcting the detected inclination of the source document image. In addition, PTL 2 discloses a method of clipping out an image from each of a plurality of source documents placed on a document table, detecting the inclination of each of the source document images, and correcting the detected inclination of the each of the source document images.